Leroy C. Stevens (1920–2015) was a scientist at

The Jackson Laboratory The Jackson Laboratory (often abbreviated as JAX) is an independent, non-profit biomedical research institution which was founded by Clarence Cook Little in 1929. It employs over 3,000 employees in Bar Harbor, Maine; Sacramento, California; Far ...

acknowledged as an early pioneer of embryonic stem cell research.

History

Stevens was born in

Kenmore, New York Kenmore is a village in Erie County, New York, United States. The population was 15,205 at the 2020 census. It is part of the Buffalo-Niagara Falls metropolitan area. Kenmore is in the south part of the town of Tonawanda, and together with the ...

in 1920. In 1942, he received his B.S. from

Cornell University Cornell University is a Private university, private Ivy League research university based in Ithaca, New York, United States. The university was co-founded by American philanthropist Ezra Cornell and historian and educator Andrew Dickson W ...

. After completing his undergraduate degree, Stevens served in the

United States Army The United States Army (USA) is the primary Land warfare, land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of th ...

in Europe, where he was awarded the

Silver Star The Silver Star Medal (SSM) is the United States Armed Forces' third-highest military decoration for valor in combat. The Silver Star Medal is awarded primarily to members of the United States Armed Forces for gallantry in action against a ...

for his bravery in action in Sicily by General

George S. Patton George Smith Patton Jr. (11 November 1885 – 21 December 1945) was a general in the United States Army who commanded the Seventh Army in the Mediterranean Theater of World War II, then the Third Army in France and Germany after the Alli ...

. When he returned to the US, he completed his Ph.D. in

embryology Embryology (from Ancient Greek, Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logy, -logia'') is the branch of animal biology that studies the Prenatal development (biology), prenatal development of gametes (sex ...

from the

University of Rochester The University of Rochester is a private university, private research university in Rochester, New York, United States. It was founded in 1850 and moved into its current campus, next to the Genesee River in 1930. With approximately 30,000 full ...

in 1952 studying under

Johannes Holtfreter Johannes Holtfreter (January 9, 1901 – November 13, 1992) was a German-American developmental biologist whose primary focus was the “organizer,” a part of the embryo essential for the development of the proper body plan. Biography Holtfr ...

. He subsequently joined The Jackson Laboratory as a postdoctoral laboratory Fellow in 1953. In 1967, he was promoted to the position of senior staff scientist at The Jackson Lab, a position now designated as professor. Stevens spent his entire professional career at The Jackson Laboratory, except a sabbatical year from 1961 to 1962 which he spent as a

Guggenheim Fellow Guggenheim Fellowships are grants that have been awarded annually since by the John Simon Guggenheim Memorial Foundation, endowed by the late Simon and Olga Hirsh Guggenheim. These awards are bestowed upon individuals who have demonstrated d ...

at the Laboratoire d’Embryologie Nogent sur Marne. Originally, Stevens' work focused on studying the harmful health impacts of cigarette paper because of tobacco company grant to C.C. Little, the founder of The Jackson Laboratory. However, in 1958 he examined a large

testicular tumor Testicular cancer is cancer that develops in the testicles, a part of the male reproductive system. Symptoms may include a lump in the testicle or swelling or pain in the scrotum. Treatment may result in infertility. Risk factors include an ...

on a mouse from the 129 strain and noticed it was composed of many kinds of tissues, including muscle, skin, bone, and hair. Over time, Stevens observed that these tumors, known as

teratocarcinoma A germ cell tumor (GCT) is a neoplasm derived from primordial germ cells. Germ-cell tumors can be cancerous or benign. Germ cell tumors typically originate from the gonads (ovary and testis), but can arise in other areas of the body. Extragonadal ...

s or

teratoma A teratoma is a neoplasia, tumor made up of several types of biological tissue, tissue, such as hair, muscle, Human tooth, teeth, or bone. Teratomata typically form in the tailbone (where it is known as a sacrococcygeal teratoma), ovary, or test ...

s, produced not only this variety of tissue types but also groups of undifferentiated cells with the capacity to grow into a wide range of tissue types. In 1970, Stevens noticed that the cell populations he was studying that gave rise to teratomas were very similar to the cells of very early embryos. Stevens called these cell types "

pluripotent Cell potency is a cell's ability to differentiate into other cell types. The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell, which like a continuum ...

embryonic stem cell Embryonic stem cells (ESCs) are Cell potency#Pluripotency, pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage pre-Implantation (human embryo), implantation embryo. Human embryos reach the blastocyst stage 4� ...

s." In order to study this phenomenon, Stevens selectively bred strain 129 to select for the teratoma tendency. Normally, such cancers are very rare but in Stevens’ new mouse strain, they were present in 1 out of every 10 mice.

Beatrice Mintz Beatrice Mintz (January 24, 1921 – January 3, 2022) was an American embryologist who contributed to the understanding of genetic modification, cellular differentiation, and cancer, particularly melanoma.Martha J. Bailey, ''American women in sci ...

and Karl Illmensee, visited Stevens to learn his techniques and use his 129 mice bred for a high rate of teratomas and used these techniques to demonstrate that the embryonic stem cells could develop not only into teratomas but also into full organisms. This work was foundational in the field of embryonic stem cells and stem cell research. Stevens' later studies focused on developing mouse models for the testing of

chemotherapeutic drugs Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) in a standard regimen. Chemotherapy may be given with a curat ...

. and retired from the Laboratory in 1989. In 2015, at the age of 94, he died of congestive respiratory failure.

References

{{DEFAULTSORT:Stevens, Leroy C. American geneticists American immunologists 1920 births 2015 deaths People from Bar Harbor, Maine Cornell University alumni